FOUNDATION INVESTIGATIONS FOR STRUCTURES

Transcription

1 FOUNDATION INVESTIGATIONS FOR STRUCTURES 6 INDEX Page I. Overview of MoDOT Practice 1 A. Geotechnical Organization of MoDOT 1 B. Types of Reports 1 C. Special Investigations 2 II. Policy Manuals 3 A. Materials Manual 3 B. Traffic Control 3 C. Safety 3 III. Performing Foundation Investigations for Structures 4 A. Objectives 4 B. Resources 4 C. General Procedures 4 1. Knowledge of Geologic Area 4 2. Site Access 4 3. Foundation Conditions 4, 5 4. Foundation Types 5 a. Spread Footings 5 b. Deep Foundations 5 c. Culverts with Floor Slab Omitted 5 d. Culverts with Compressible Foundations 5 e. Retaining Structures 6 f. Spill and Channel Slopes 6 g. Special Investigations 6, 7 D. Division of Responsibility 7 E. Practical Considerations 8 F. Philosophy 9 IV. Technical Guidelines for Geotechnical Investigations 10 A. Bridges Deep Foundations (Piling) 10 a. Boring Interval 10 b. Split-Spoon Sampling Interval 10 c. Borings in Shale 10 d. Borings in Rock 10 e. Augering 10 i. Northern Missouri or Bootheel 10 ii. Central Missouri 10 iii. Bootheel 10 iv. P.A.W.T. 10 f. Eliminating Borings in Waterways 10 g. Samples 10 i. Atterberg Samples for Geotextile Recommendations 10 ii. Seismic 10

2 Page 2. Shallow Foundations 10 a. Spread Footings 10 b. Eliminating Borings in Waterways 11 c. Samples 11 i. Atterberg Samples for Geotextile Recommendations 11 ii. Seismic Drilled Shafts (excluding major river and lake crossings) 11 a. Boring Interval 11 b. Amount of Core Required 11 c. Samples Drilled Shafts (major river and lake crossings) 11 a. Boring Interval 11 b. Amount of Core Required 11 c. Samples 11 B. Walls MSE (Mechanically Stabilized Earth) or Cantilever 11 a. Boring Interval 11 b. Sampling Interval 11 c. Sampling Rocky Soil 11 d. Soft Foundations 11 e. If Rock is Encountered Above Footing Elevation 11 f. Auger Holes Cantilever 12 a. Amount of Rock Core Sound Walls 12 a. Boring Interval 12 b. Split-Spoon Sampling Interval 12 c. Amount of Rock Core 12 i. Rock Encountered Within 5' to 10' Below Bottom of Wall 12 ii. Rock Less than 5' from Bottom of Wall 12 d. Augering 12 i. Locations 12 ii. Depths 12 C. Box Culverts Investigations for Using Rock as the Floor of the Culvert 12 a. Rock More than 5' Below Flow Line 12 b.. Rock Less than 5' Below Flow Line 12 c. Augering Culverts with Compressible Foundations 12 a. Boring Interval 12 b. Sampling Interval 12 c. Samples 12 D. Light Towers Boring Interval Split Spoon Sampling Interval Amount of Rock Core 12 a. Rock Within 20' of Finished Ground Line 12 b. Rock More than 20' Below Finished Ground Line 12 ii 7

3 8 V. Special Foundation Investigations 13 A. Slide Investigations Photograph Slide Survey Entire Area Note Seepage Identify Slide Limits Inspect Drainage Structure Note Fences, Trees, and Power Poles Cross Sections of Slide Area Augering 13 a. Depth of Disturbed Material 13 b. Texture of Material 13 c. Water Table 13 d. Set Wells Samples Water Tables Note Possible Corrective Measures 14 a. Drainage Patterns 14 b. Material Supply 14 c. Where Can Material Be Wasted 14 d. Right-of-Way Slide on Active Construction Job 14 a. Determine Natural Ground Line 14 b. Sample Fill 14 c. Set Hubs Inclinometers 14 a. Use 14 b. Where 14 c. Backfill 14 Page VI. Sampling Techniques 15 A. Introduction 15 B. Pocket Penetrometer 15 C. Field Moistures 15, 16 D. Torvane 16 E. Sample Length 16 F. 3" and 5" 16 G. Tube Push Length 16 H. Sample Wrapping 16 I. Handling Samples 17 J. Waxing Samples 17 K. Storing Samples 17 L. ASTM Classification Samples 17 M. ASTM Visual Classification 17 N. Log Samples in Log Book 18 O. Mark Sample Sheets 18 P. Assign Samples for Testing Immediately 18 iii

4 9 Page VII. Field Logs 19 A. Log Sheets 19 B. Locations 19 C. Elevations 19 D. Water Tables 19, 20 E. Descriptions and Notes 20 F. Question Marks on Logs 20 G. Note Anything that Would Effect the Constructability of the Structure 21 VIII. Diaries 22 A. Introduction 22 B. Format 22 C. Sample Log Format 22 IX. Seismic Investigation 23 A. Introductions 23 B. Sampling Procedure 23 C. Samples Needed 23 D. Reporting 23, 24 X. Soil Surveys 25 A. Sampling and Testing 25 B. SCS Soil Series Names 25 C. Slope Selection Chart 25 D. Spill Slopes 25, 26 E. Spill Slopes in Cut Sections 26 F. Rock Slopes in Cut Sections 27 XI. Appendix 28 A. Missouri Modified Standard Penetration Test 28 B. Soil Classification Guide (Cohesive) Plasticity Chart 30 C. Soil Classification Guide (NON-Cohesive) 31 D. Rock Classification Guide 32, Field Identification System for Rock Classification RQD Core Handling and Labeling Symbols for Rocks and Soils 37 E. Atterberg Limits and Expected Erosion Potential 38 F. Correlations of Strength Characteristics 39 G. Example Forms Bridge Logs 41, Auger Logs 43, Seismic Summary Sheet 45, 46 iv

5 1 I. OVERVIEW OF MoDOT PRACTICE A. Geotechnical Organization of MoDOT Geotechnical functions in the Missouri Department of Transportation (MoDOT) are performed by personnel assigned to the Materials Engineering Unit, both in the district and at the General Headquarters in Jefferson City. Each of the ten districts has a District Geologist or District Soils and Geology Technologist who reports to the District Operations Engineer. At the division/unit level, these functions are administered through the Geotechnical Section. The district geologist's most important job is the performance and reporting of the soil survey. Basic functions of the soil survey include typing soil and rock materials and determining their limits and engineering characteristics. Other important responsibilities are obtaining preliminary bridge foundation information and identification of potential foundation problems which should be investigated in more detail by division/unit level personnel assigned to the Geotechnical Section. These are referred to as, for lack of a better term, "Special Investigations." The Geotechnical Section has a specialized soil laboratory with technicians and equipment for performing consolidation tests, various forms of shear tests, and other specialized soil tests. Professional level employees with academic backgrounds in Geology and Civil or Geological Engineering concentrate on one or more specialties. A drilling subsection assigns equipment and personnel statewide as needed by either District or General Headquarters staff. The section does all final foundation investigations for structure layouts prepared by the Bridge Unit's Preliminary Engineering Section and all of the settlement and stability investigations referred to it by the districts. Other duties include slide investigations, work on subgrade and base stabilization, geophysical explorations, research activities, and "other duties as assigned." The drilling section employs its own staff of field drilling personnel and drilling support equipment. Drilling equipment includes Mobile B-31 combination power augers and pavement drills, a pavement drill, Failing 1500 core drills, a CME 850 all-terrain unit, CME 45 truck mounted unit for environmental investigations, and track mounted Simco Versa Drills. A portable barge is available to support one of the smaller drills for use on small lakes and streams. B. Types of Reports 1. The soil survey report touches on foundations by pointing out possible foundation problems. It also contains basic slope recommendations which affect bridge length, soil types and properties for pavement design, depths to rock and type of rock for determining cut quantities, and cut slope recommendations for soil and rock. 2. The preliminary bridge foundation report, which is submitted by the district as an adjunct to the soil survey report, is usually furnished to the Bridge Unit for their guidance in preparing preliminary bridge layouts and to the Materials Engineering Unit for guidance in conducting a more detailed foundation investigation. (Preliminary borings for such reports may be omitted where access problems are especially difficult.) 3. The final foundation investigation report for structures starts with a formal request from either the Bridge Unit or District following procedures in FS-25 of the Materials Manual. The Bridge Unit or District provides a preliminary layout and a suggested boring plan. This boring plan typically will call for a core and/or standard penetration boring at every other bent with auger borings at the remaining column locations. By prior agreement, it is understood that this suggested boring plan is only a guide which will be modified as deemed necessary. The Geotechnical Section only rarely makes recommendations for specific foundation types. The basic aim is to furnish the Bridge Unit or District with the information needed to develop designs for those foundation types practical for a particular site. Rules of thumb as to what is practical have been developed jointly by the Geotechnical Section and the Bridge Unit. These are discussed elsewhere in this document.

6 C. "Special Investigations" So-called "special investigations" usually pertain to embankment settlement and slope stability problems. Normally the district identifies potential problems during the soil survey and requests the Geotechnical Section to investigate. In some cases, the problem may not be identified until the final foundation investigation is made for the structure. This is late in the game from a design standpoint, but much better than finding it under contract. The recommendations made as a result of these investigations may influence structures in various ways; bridge length may be affected, end fill slopes and culvert camber, etc. The most common effect is on construction sequence and rate of construction. Piles should not be driven in an embankment until it has stopped settling and until excess foundation pore pressures have dissipated. For embankments, i.e., roadway items, very specific recommendations are made as to remedial courses of action rather than saying here is the problem and leaving it to the designer to figure out a solution. However, more than one solution may be technically feasible and it should be realized that other considerations, such as economics, may dictate which solution is actually chosen. Face-to-face meetings with the concerned designers before a report is issued are important to permit mutual exploration of the problem and the ramifications of possible solutions. 2

7 3 II. POLICY MANUALS A. Materials Manual [References not included except 1(a)] 1. Field Section 21 - Soil Survey (a) Explanatory Comments on Use of the Slope Selection Chart (included) 2. Field Section 22 - Release of Subsurface Information 3. Field Section 23 - Drilling Operations 4. Field Section 25 - Final Soundings for Structures 5. Field Section 26 - Special Foundation Investigations 6. Field Section 27 - Slide Investigations 7. Field Section 28 - Quarantine Regulations 8. Lab Section 21 - Soil Survey 9. Lab Section 22 - Soils and Geology Laboratory Testing 10. Lab Section 28 - Quarantine Regulations B. Traffic Control (References not included) 1. FHWA - Manual on Uniform Traffic Control Devices 2. Division of Maintenance and Traffic - Traffic Control for Maintenance Operations C. Safety (Reference not included) 1. MHTD - Handbook of Safety Rules and Regulations

8 4 III. PERFORMING FOUNDATION INVESTIGATIONS FOR STRUCTURES A. Objectives 1. Develop subsurface information adequate to permit design of any technical and economical type of structure foundation for the site under investigation. 2. Develop subsurface information adequate to evaluate stability and deformation potential of embankments and proposed slope templates in the structure area, including walls and channel slopes, if not already addressed by prior investigations. 3. Develop subsurface information adequate to evaluate need for special erosion protection measures necessary to protect the proposed construction. B. Resources 1. Preliminary Bridge Report 2. Soil Survey Report 3. Foundation Investigation Reports for Old or Adjacent Structures 4. As-Built Plans for Old or Adjacent Structures 5. Special Foundation Investigation Reports 6. Geologic and Topographic Maps 7. Air Photos C. General Procedures The first step after receipt of a request from the Bridge Unit or District is a file search for soil survey reports, preliminary bridge reports, and foundation reports for adjacent structures. A packet of information, which includes plans, correspondence, and prior reports is assembled for field use. Next, the district is consulted for advice as to field conditions, problems with utilities, crops, landowners, etc. If site access conditions are especially bad, someone from the Geotechnical Section may visit the site to determine what equipment may be needed and how the site can be reached. As noted previously, either the Bridge Unit or the District's boring plan may be modified as appropriate given site conditions and constraints. Some of the considerations here include: 1. General knowledge of conditions in the physiographic or geologic area where the work is to be done. This strongly influences the kind of investigation which should be performed and how detailed it should be. For example, in the Springfield area, residual clay over heavily pinnacled rock is likely and the most important thing is to map the rock surface irregularities with a lot of auger borings to rock so that point bearing pile lengths can be determined. In the bootheel area, auger borings are virtually worthless and standard penetration test borings for design of friction piles are most important. 2. Site access conditions are a very practical consideration. It may just not be feasible to drill a hole in the middle of an urban interstate highway and it may be extremely difficult and/or expensive to drill one in the middle of a river. That is where judgments must be made about how necessary that particular boring is -- can conditions be reasonably extrapolated from offset borings, would geophysical methods work as well, etc. In many cases, the borings can be omitted with little risk. In other situations, considerable expense and trouble may be justified to get on location. This may involve a different type of equipment, hiring a bulldozer, mobilizing the portable barge, or temporarily blocking a lane of roadway. The most extreme access problems involve major river or lake crossings where barges, tugs, and support services must be provided by contract. 3. The third consideration involves foundation conditions actually encountered as the investigation progresses. This is a principal reason why all MoDOT foundation investigations are supervised in the field by trained personnel. If conditions encountered are different than anticipated, it is expected that the scope of the investigation will be adjusted as necessary to fit actual conditions.

9 4. As previously noted, the Geotechnical Section rarely makes recommendations for specific foundation types. The basic aim is to furnish the Bridge Unit with the information needed to develop designs for foundation types practical for a particular site. Several rules of thumb are helpful in deciding what is practical. For example: a. Spread footings Spread footings for bridges will not be considered unless foundation material has an unconfined compressive strength of 3 tsf or more, and such material is within a fairly shallow depth. If firm material is 10 feet or more below final grade line, then piles will be used. b. Deep Foundations MoDOT guidelines used to estimate how far to carry standard penetration tests for design of friction piles are 30 continuous feet of bearing strata with an N 60 value of 20 or greater. It is normal practice to drill half again as deep, or at least 100 feet in any case, to check depth to rock for a point-bearing option. Point bearing is usually a feasible option almost everywhere in the state except in the southeast lowlands or "bootheel" area where sands extend to depths of several thousand feet. Even here, however, a careful check must be made for the possible presence of soft clay layers within and just below the range of probable friction pile penetration. c. Culverts with Floor Slab Omitted Large box culverts may be built more economically if a floor slab can be omitted. The Bridge Unit feels this is generally feasible if rock is within five feet of flowline. So, where rock may be shallow, an attempt is made to drill auger holes every 25 feet or so along each proposed wall. An attempt is made to judge the durability of the rock based on inspection of exposures and cores and knowledge of past performance of particular formations. The rock should have an RQD equal to or greater than 75 and should not be thin bedded. If rock is deeper, only a few auger borings to verify this fact may be sufficient. d. Culverts with Compressible Foundations Culverts, if built over compressible foundations, may require special investigations based on undisturbed sampling to determine need for camber to compensate for settlement and to assess the danger of joints opening due to spreading caused by settlement. In some areas of the state where this is a particular problem, structural collars are sometimes recommended around joints to control spreading and faulting and piping of silty soils into opened joints. 5

10 6 e. Retaining Structures For retaining structures, information is obtained for determination of allowable footing bearing pressures and angles of internal friction of the materials to be retained and the foundation material. The latter is done by correlation to Plasticity Index (PI) for walls of low height (using the average correlation less one standard deviation), Appendix F, and by drained shear testing for higher and more critical structures. In some cases, it may be necessary to obtain undisturbed samples for testing in order to evaluate overall stability of the slope of which the wall will be a component. By agreement with the Bridge Unit, evaluation of global or overall stability is a Geotechnical Section responsibility. If inadequate global stability is likely, possible solutions are evaluated - such as lowering the base of the wall, increasing the width to height ratio and excavation and replacement with rock fill, etc. f. Spill and Channel Slopes The Geotechnical Section attempts to furnish overall guidance on prudent slope selection. This was done first by development of criteria, based on soil type and geologic origin, which is used by the district geologist in making project slope recommendations. Secondly, a review is made, often by specific request of the Bridge Unit, of the adequacy of embankment stability in the vicinity of the bridge ends, particularly at stream crossings. Geotechnical recommendations may affect bridge length, the fill end slopes, and erosion control measures for the channel banks. Often, for example, evidence will be found of channel bank failures which reflect a need for bank stabilization or bridge lengthening.

11 g. Special Investigations These investigations were discussed in Section I where it was noted that, while normally initiated by the district as part of the soil survey, a problem may not be identified until final bridge soundings are being done. Undisturbed foundation sampling is done or supervised by a geologist, engineer, or senior technician. Large diameter samples are strongly preferred -- often of 5-inch diameter, although 3-inch diameter samples are also commonly taken. In very soft soils, piston samplers are used in lieu of the normal Shelby tubes. Continuous undisturbed sampling is preferred, with frequent use of a 5-inch sampler, then a 3- inch sampler, followed by pushing a split spoon for inspection before cleaning the hole and restarting the cycle. MoDOT practice differs from that of many agencies in that soil samples are routinely extruded in the field. This permits thorough inspection and logging, obtaining field moisture and Atterberg Limits Classification samples, and preliminary field testing with the Torvane and Pocket Penetrometer. Most important, it permits the technical supervisor to develop a good feel for the problem as the investigation progresses. Samples are selected and designated at this time for certain types of testing, wrapped in foil, and sealed in wax in cartons for transport back to the lab. For a typical problem involving an embankment settlement and stability problem, the lab testing program will include moisture contents, Atterberg limits, consolidation tests, unconfined compression, and drained, direct shear tests, all supplemented by Torvane and Pocket Penetrometer tests. Stability analyses are performed using a computer program, either circle analysis (Bishop), block and wedge (Spenser), or both as may be most appropriate for particular circumstances. Total strengths are used to assess the initial or rapid construction case. Effective stress analyses are used to assess fully consolidated conditions as well as intermediate degrees of consolidation. This data can be interpreted to assess the need for controls on rate of construction. Amount of settlement estimates have been found to be fairly accurate. Actual rates of settlement are usually, but not always faster, than predicted. If a predicted time of settlement appears critical, office calculations are checked by doing field permeability tests and back figuring coefficients of consolidation. Usually, field perms will indicate much faster drainage, but sometimes agree very well with predictions based on laboratory tests. Before using vertical sand drains or any very expensive solution, field permeability testing should be done. D. Division of Responsibility 1. The Bridge Unit or District prepares a sounding layout with a suggested boring plan. 2. It is the geotech's responsibility to adjust or modify that plan as necessary to accomplish the objectives previously outlined, based upon the site conditions and practical access problems which may be encountered. 3. The geotech should identify and investigate any geotechnical problems which may preclude or adversely affect the proposed design and be prepared to offer recommendations for alternative designs or design modification. 4. Retaining walls. The Bridge Unit or District is responsible for checking all aspects of structural (internal) stability and for evaluating external stability with respect to overturning, sliding (at the base of the wall) and bearing failure. The Geotechnical Section is responsible for furnishing the data inputs necessary for the external stability checks and for evaluating overall or global stability included slopes for which the proposed wall may be a component. 7

12 5. Bridges. The Bridge Unit will design the foundation units in almost all cases but may ask for design assistance in certain instances. It is the geotech's responsibility to furnish data inputs of the type and quantity required to design those foundation types which are technically and economically feasible at each site. This infers that the geotech must have the capability and knowledge, and must have developed the information necessary to design the foundation if requested to do so. Keep in mind that a foundation cannot be designed in isolation. You can design an individual pile or footing but you must also know column and bent loads, group or cluster effects, embankment "drag loads", etc. and understand the interactions of the resulting stresses. 6. Allowable Bearing. "Allowable bearing" is not an intrinsic soil property but rather is a value based upon intrinsic soil properties as influenced by a specific arrangement of specific types, dimensions, and loadings of foundation units and the resulting distributions of stresses. It is not to be confused with "presumptive bearing values" or any specific measure of soil strength. While in most instances the distinction may seem academic, it can be a critical distinction. Examples: (1) A single square footing will have a different "allowable bearing" than a strip footing or a rectangular footing and that of either type may be adversely affected by the proximity of another bearing unit. (2) Similarly, the capacity of a single friction pile or a single earth anchor may be reduced by the proximity of similar units. In any case, "allowable bearing" is influenced not only by the factor of safety against failure (the usual criterion) but also by considerations of allowable deformations in the structure. The underlying reason why higher factors of safety against bearing failure are utilized than for other failure modes is to limit deformation. Keeping unit loads near the unconfined compressive strength (not in excess of about 1.2 Qu) keeps loads at or below the preconsolidation value of the soil. 8

13 E. Practical Considerations 1. "Proofing" of Foundations. This touches on how foundations are actually built. If point bearing piles are used, the adequacy of the rock supporting the tip is "proofed" in excess of in-service loads by the dynamic stresses associated with driving the pile so there is relatively little cause for concern about the possibility of a void or cavern beneath the pile tip. This affects the conduct of the foundation investigation. A core may be irrelevant and it may be sufficient to rock bit five feet or so into rock in a couple holes and simply auger to rock (augering deep enough to be sure it's not a boulder) in the rest of the borings - even omitting many holes if rock is deep and of relatively constant elevation. Footings and drilled shafts on the other hand are loaded statically as the bridge is built. "Proofing" must be done by borings, either during the foundation investigation or as a construction requirement after the excavation is completed and prior to placing steel or pouring concrete. Drilled shafts often have very high unit loads so cores and even compression tests of the recovered core may be important, especially with weaker rock types. In hard rock, both cored and rock-bitted holes should be advanced to a significant depth below probable tip elevation to detect possible cavities or soft zones. Of course, if the exact location of the drilled shaft is unknown, only a few deep borings may be sufficient for preliminary design providing the contract is structured to require confirmation borings at each shaft location during construction. 2. Construction Problems. In most cases, investigative techniques are clear cut and the scope of the investigation may be less detailed when only one type of foundation is feasible. However, the scope of investigation should be influenced by considerations of the possible consequences of a change in foundation type during construction. If spread footings on rock are anticipated but no rock is found at one column, then a pile driver must be brought in. If there is no bid item for that type of work, then the price must be negotiated. The contractor will likely ask for an additional working day and claim severe impact costs, etc. For these reasons, more thorough work (at least in numbers of borings) are needed where spread footings are anticipated than for most other foundation types. Of course, being shallow, the borings should be completed more quickly. The reverse circumstance is less critical. If piles are planned and a suitable bearing stratum for footings is found on one bent, it is a simple matter to form and pour the footing while under running the piles at that location. This also has implications with respect to the scope of the foundation investigation. There is often little risk in omitting holes when piles are the logical foundation type and subsurface conditions appear uniform. 3. Footings on Hard Rock. For most simple structures, spread footings on hard rock will be of some practical minimum size such that unit loads will usually be 10 tsf or less and almost never in excess of 20 tsf. This is one reason why strength tests on hard rock are usually rather pointless and judgments on hard rock allowable bearing capacities are subjective, sometimes involving building code tables, RQD, and other empirical means. Keep in mind that the discontinuities of rock (bedding planes, joints, etc.) and, in particular, any loss while coring represent the real bearing limitations of that rock. You must rely on the driller's judgment as to why you didn't recover core. If the drill stem dropped quickly with little or no resistance, you have a void, a clay seam, or other soft material. Footings on soft rocks such as clay shales, claystones and even some sandstones and siltstones are another matter. Here the normal allowable bearings may be within a much lower range, requiring substantial enlargement of footings. In such cases, fairly detailed test data (SPT, Qu, and even pocket penetrometer data) may be needed to make judgments about allowable footing loads. 9

14 F. Philosophy Philosophy may seem out of place in a technical guideline. Call it our "organizational culture" if you want to be more in vogue. 1. THE BORING LOG IS SUPPOSED TO FURNISH USABLE FOUNDATION ENGINEERING INFORMATION. Any geologic, pedologic, or mechanistic factors influencing or contributing to the desired information are of importance. However, it is difficult to visualize what interest a bridge designer might have in a description such as: "A dark gray to black stratum of Willow Pond shale, fissile, containing lingulas, conodonts and various species of brachiopods." Similarly, describing a soil as "dark blue, moist, alluvial Tippecanoe montmorillonitic clay, mottled rusty red, derived from podsolic soil group" is mostly gobbledygook as far as a bridge designer is concerned. Emphasis should be concentrated on such engineering information as will be of value to the designer, regardless of the geotech's interest in micro- or macrofossils, fine distinctions in color shades, etc. For proper perspective, it should be kept in mind that the final aim is to build a bridge. 2. How much information is enough? Answering this question involves a number of considerations. You must keep in mind the logistical overhead in getting you to the job. Property owners and utilities have been cleared; a survey party has staked the job; equipment has been scheduled and travel time committed to and from the job. Obviously you should take time to do it right. The geotech is the one individual on the job with the knowledge and responsibility to ensure the job is complete. It's important that you accept ownership of the investigation as a personal responsibility to satisfy the department's and your own objectives in performing the work. 10

15 IV. TECHNICAL GUIDELINES FOR GEOTECHNICAL INVESTIGATIONS A. Bridges 1. Deep Foundations (Piling) a. One Penetration hole per two bents. Example 4 bent bridge - 2 penetration holes. b. Begin at the surface and run penetration tests every 5 feet until 30 continuous feet of 20 blow count or better of bearing strata is encountered. After bearing is achieved, continue penetration tests at 10 foot intervals until rock is encountered or boring is advanced to 100 feet. Core or rock bit 5 feet of rock or shale. (Should adequate bearing be at a deep depth, it may be cheaper to use point bearing piling placed on rock. This is why we need at least 1 boring to establish rock elevation). c. If shale is encountered and adequate bearing is not achieved in the overburden, run S.P.T. on top of shale, core 5 feet, run S.P.T., core 5 feet and run S.P.T. (This method of shale penetration and core can be modified if the engineer/geologist retrieves an adequate shale sample to run a Qu test. If a good sample of shale is retrieved, eliminate the penetrations at the middle and end of the core runs.) d. If rock is encountered and adequate bearing is not achieved in the overburden, core10 feet of rock. e. Augering i. Northern Missouri or Bootheel - Take boring at least to 100 feet if bedrock is not encountered. Other auger borings should be taken down to the depth where bearing is achieved as determined by the S.P.T. (Should adequate bearing be at a deep depth, it may be cheaper to use point bearing piling placed on rock. This is why we need at least 1 boring to establish rock elevation.) ii. Central Missouri -- Normally make borings to bedrock and make pattern holes if the top of rock is uneven (more than 5 feet difference in rock elevation within one bent), especially for spread footings. iii. Bootheel -- Auger some bents at least 20 feet below where bearing was achieved based on S.P.T. Check for any possible soft layers that may exist below bearing strata. iv. P.A.W.T. - Pushed Auger Without Turning - describes a soft condition and should be noted on any log where this is done. f. When eliminating bents due to bents falling within the waterway, make sure to penetrate until n values of greater than 20 are found for 25 or 30 consecutive feet below the elevation of the stream bed. g. Samples i. Atterberg samples of final grade surficial materials are required for geotextile recommendations on stream crossings. One sample on each side ii. of the stream or river is adequate. Bridges located in seismic zones require earthquake sampling (see Earthquake Sampling, Page 22). 2. Shallow Foundations a. Spread footings on some or all of the intermediate bents will normally be used if the top of rock is no more than 12 feet below finished grade. Therefore, at least 10 feet of good core (RQD 75 or higher) should be acquired on the intermediate bents. It is important to make borings on all bents where this condition exists. Piling is normally used on the end bents except where the bridge end is positioned on a rock bluff. 11

16 b. When eliminating intermediate bents in waterways where rock is within 5 feet of stream bottom elevation, 15 feet of core below stream bottom elevation is needed. On major rivers, borings will normally be based on the type of footings that are planned (drilled shafts or spread footings). Always run S.P.T. in the overburden to aid contractor in driving coffer dams or drilling for shafts. c. Samples i. Atterberg samples of final grade surficial materials are required for geotextile recommendations on stream crossings. One sample on each side of the stream or river is adequate. ii. Bridges located in seismic zones require earthquake sampling (see Earthquake Sampling, Page 22). 3. Drilled Shafts (excluding major river and lake crossings) a. Minimum of one core hole per bent for small structures and for larger structures in uniform geology. One core hole per column for larger structures in non-uniform geology. b. Minimum of 25' of core in rock and 30' in shale. i. Ex: For end bearing on rock and a 6' shaft. The top 5' of rock is not counted. 5' rock socket. For end bearing you need to go 2 X diameter below the rock socket, 12' =22' say 25'. c. Need Qu's for design of the rock socket. 4. Drilled Shafts/River Borings ( major river and lake crossings) a. Minimum of one core hole per column except for drilled shaft groups where 5 core holes per bent will be required. b. Minimum of 40' of core in rock and 50' in shale. c. Need Qu's for design of the rock socket. B. Walls 1. MSE (Mechanically Stabilized Earth) a. Sample about every 200' with shelby tubes. Two sample holes per wall minimum. Try to sample where the wall is the highest. b. Take undisturbed soil samples to at least 10 feet below footing elevation for Qu, Direct Shear, and Atterberg limits. Need to find internal angle of friction for retained and foundation material. If retained material is fill, get internal angle of friction from soil survey. If sand is encountered, take samples for gradations and atterberg limits as appropriate (seismic). c. If soil is too rocky to use shelby tube, penetrate every 2 1/2' at least 10 feet below footing elevation. Take Atterberg samples, moisture samples, and pocket penetrometer readings. d. If foundation material is too soft to use shelby tubes or osterberg sampler, run S.P.T. at 2.5 foot intervals for at least 10 feet below footing elevation. If still soft, go to 5 foot increment. May use cantilever wall on piling. Rock bit or core at least 5 feet of good rock or shale. e. If rock is encountered above footing elevation or before you sample 10' below bottom of wall, core a minimum of 5 feet below bottom of wall for MSE wall and 10' minimum below bottom of wall for cantilever wall. f. Auger holes are usually laid out about every 25'. If you are in uniform soil and rock is more than 5 feet below the footing elevation, you can skip every other hole. Auger about 10' below bottom of wall or a little deeper if you suspect rock is close. 12

17 2. Cantilever Walls or Spread Footings a. Do similar to MSE wall except if rock is near footing elevation and wall may be set on rock, take 10 feet of core (depending on wall height, 5' of good rock may be adequate) and if shale, run Qu's. 3. Sound Walls a. Use S.P.T. and 3" shelby tubes to sample a hole about every 200 feet of wall length. b. Push 3" shelby tube 2.5 feet followed by the split spoon sampler. c. Run S.P.T. and shelby tube on the first 5 feet interval below bottom of wall. Take Qus (for determination of allowable bearing), Atterberg samples, moisture samples, pocket penetrometer readings and torvane readings. d. Continue to run S.P.T. at 2.5 intervals for at least 20 feet below bottom of wall. Take Atterberg samples, moisture samples, and pocket penetrometer readings. e. Amount of Rock Core. i. If rock is encountered within 5 to 10' below bottom of wall, core 5'. ii. If rock is less than 5' from bottom of wall, core 10'. f. Augering i. Locations same as MSE walls. ii. Auger 25' below bottom of wall. C. Box Culverts 1. Investigations for Using Rock as the Floor of the Culvert a. If rock is encountered deeper than 5' below flow line, drill enough holes to makesure rock does not come up to within 5 feet of flow line. b. If rock is encountered within 5 feet of the flow line, core a minimum of 2 holes per culvert. Usually one core hole on each side of the road. Core a minimum of 10'. c. If rock is encountered within 5 feet of the flow line, auger every 10' for each wall in the box culvert (i.e., double box: 3 walls; single box: 2 walls, etc.) 2. Culverts with Compressible Foundations a. Usually one boring on each side of the stream crossing is adequate. The boring locations should be close to the stream and under the highest part of the proposed fill. b. Sampling should be continuous shelby tubes unless material is too soft, then the Osterberg sampler should be used. c. Samples required are 3" for consolidation tests and unconfined compression. Either 3" or 5" for Direct Shear and soil samples for Atterberg test. moistures, pocket penetrometer, and Torvane should also be obtained. 13

18 14 D. Light Towers 1. Use S.P.T. and 3" shelby tubes to sample one hole per tower. 2. Push 3" shelby tube 2.5 feet followed by the split spoon. 3. Clean out to the next 5' interval and repeat the procedure. 4. Alternate S.P.T.s and 3" shelby tubes for at least 30' below finished ground line. Take Qus (undrained shear strength), Atterberg samples, moisture samples, pocket penetrometer readings, and torvane readings. 5. In either cohesive or cohesionless soil, perform SPT test at 35 and 40 to complete the boring. Take Atterberg samples, moisture samples, and pocket penetrometer readings. 6. If the soil is too rocky to use the Shelby tube, split spoon on 2.5 foot intervals to achieve a depth of 30' below finished ground line and then penetrate again at 35 and 40 to complete the boring. 7. Amount of Rock Core. a. If rock is encountered within 20' of finished ground line, core 10'. b. If rock is more than 20' from finished ground line, core 5'. b. If rock is more than 20' from finished ground line, core 5'. Tower borings will need to be reported on a bridge log for spt s and core log and a summary sheet for p-y parameters and electro-chemical parameters. Cohesionless soil (Sand) 1. Friction Angle from Bowles 1977 using corrected Blow Count (N1)60 (N1)60 = CnN60 (N1)60 = N60 corrected for effective Overburden Pressure Cn = correction factor for Overburden Pressure (Peck et. al.1974) 2. Relative density from either DM or FHWA/RD-86/102. DM 7.1 probably a better value because it accounts for effective overburden pressure. Cohesive soils 1. Undrained Shear Strength- USS or C from Bowles 1977 using uncorrected blow count N60, preferably Qu/2. 2. Friction Angle from correlation of PI to angle of internal friction minus one standard deviation as published in Navdocks DM-7. P-Y Curve Parameters 1. K(f) = slope (variation) of linear subgrade modulus. From Section 6.1 of the Bridge Manual or Soil Properties (Lpile & Com624P) 2. K(f)cyclic = for cyclic loading 3. E50 = strain at 50 % of the maximum difference in principal stresses, unitless, from Qu test and Section 6.1 of the Bridge Manual or Soil Properties (Lpile & Com624P) Electro Chemical Parameters Resistivity is a function of the chloride ion and sulfate ion content and most of the time we will not run this test. To run the test we need about half a materials sack and the sample is entered into site manager.

19 15 V. SPECIAL FOUNDATION INVESTIGATIONS A. Slide Investigations 1. Photograph slide and improvements effected by the movement such as culverts, bridge ends, utility poles, guard rail, pavement, fences, etc. Also, a good set of field notes should be kept. All written matter should be appropriately dated and identified. 2. Survey entire area, leave no stone unturned (walk out area). 3. Make notations concerning seepage, type of vegetation, etc. Locate seepage on sketches of plan and profile of slide. 4. Identify slide by station limits. If station numbers are not available, reference slide, soundings, and other pertinent information to the nearest crossroad drainage structure or bridge end. One of the 4 compass points can be used to describe the offsets. Final plans can then be acquired and station numbers assigned to the various field notes. Field notes should include what the offsets are referenced to such as CL lane, CL median, edge of pavement, baseline, etc. 5. Drainage structures should be inspected to determine if slide is deep seated and if structure replacement is necessary. (Measure distance from end of structure to major cracks or to any open joints.) 6. Note leaning fences, trees, and power poles. Note the direction they lean. Rows of steel fence posts may be placed on the slope or slide area to detect further movements. 7. Besides cross sectioning the slide area, at least one cross section should be taken at each end of the slide on the undisturbed slope. The spacing and number of sections taken in the slide area should be determined by the length and uniformity of slope and slide. Sections should extend out far enough to implement possible repairs. 8. Power auger soundings should supply the following information: a. Depth of disturbed material, especially for shallow slides. (Deep seated slides may require sampling as well as auger soundings to determine depth of slide.) Enough points should be drilled on the cross section to determine the location of the slide plane with reasonable accuracy. The location of the slide plane may be determined by pushing the auger. The scarp(s) of the slide should be plotted on the cross section as well as the sounding information to determine if a logical slide plane can be drawn. Additional soundings can be made at this time if necessary. b. The texture, color, and consistency of all materials should be logged. (The term "till" should be used in the log where appropriate along with the texture and consistency.) c. Water table reading should be taken after the hole has been drilled and again the following day, if possible. (For fill slides, water tables should be established on the shoulder, slide, and toe of slide. For backslope slides, water tables should be established back of the cut and on the slide.) It is suggested that 4 inch holes be drilled to establish water tables. Perforated galvanized down spout can be used to hold holes open. d. Artesian pressures should be determined where applicable. Well points should be placed in those zones suspected of carrying water. These can be made cheaply by sawing slots in PVC pipe and setting the slotted end section in a sand chamber sealed with bentonite. 9. Undisturbed samples should be taken for the following tests for all slides: a. TV and P.P. b. Direct Shear c. Atterberg Limits d. Moisture 10. Water tables should also be recorded for core drill holes. Make a notation if bentonite is

20 used and record dates and times of readings and the date the hole was drilled. 11. Make notes pertinent to possible corrective measures. Some items to be considered are as follows: a. Will possible repairs change drainage patterns or should drainage be changed to protect repaired slide area. Will alterations cause damage to private property. b. Can adequate materials be obtained nearby to repair the slide. (Can suitable soil be acquired from adjacent backslopes for slope flattening.) c. Where can disturbed material be wasted. d. If additional right-of-way is needed, what type of property will be involved. 12. Procedure for investigating a fill slide on an active construction site may be somewhat different especially if the type of slide (fill failure or foundation failure) cannot be determined by visual observation. a. Sample through fill and determine elevation of natural ground and compare it with original ground line shown on plans or ground line outside construction limits. b. Sample fill and foundation to determine the preconsolidation pressures as well as those tests listed under item number 9. (If foundation soil is over consolidated then failure is probably confined to fill.) c. Set hubs near toe of fill and on the distressed fill and record the offsets and the elevations. (If hubs on fill move independent of hubs at toe of fill, this may indicate fill failure. Should all hubs move, this may indicate foundation failure.) 13. Inclinometers may be installed to determine the depth of the failure surface and rate of slide movement. a. Inclinometers are typically installed on larger slides or on slides that are not of immediate concern and allow time for monitoring of the slide movement. Inclinometers may also be installed on active construction jobs if potential slope failure is of concern. b. Inclinometers should be installed in the slide mass and should extend a minimum of 15 feet below the anticipated failure surface. c. Inclinometers should be installed in a hole backfilled with grout although sand backfill is acceptable. The sand backfill is not as sensitive to movements as the grout. 16

21 17 VI. UNDISTURBED SAMPLING TECHNIQUES A. Introduction Undisturbed Sampling refers to obtaining soil samples using either shelby tubes or the osterberg. We take continuous samples and all usable samples should be wrapped and transported to the lab. The general procedure for the Failings and CME is to push a 5" shelby followed by a 3" shelby. The hole is then cleaned out and the process is repeated. Under no circumstances should continuous 3" shelby's be used since this leads to sample disturbance. If the soil becomes too rocky to use the shelby tube, disturbed samples may be obtained by using the SPT-Spoon. The Simco Versa Drill can only push 3" shelby tubes. No more than 2 tubes should be pushed before you require the driller to clean out. In swelling or caving soils it may be necessary to clean out after every push. In soft to medium stiff soils, pocket penetrometer 0.5 or less, it will be necessary to use a piston sampler such as the Osterberg sampler. B. Pocket Penetrometer 1. Firm, SLOW, constant push. 2. Take more than one (1) reading on a sample (average values). 3. The pocket penetrometer is a useful tool but has definite limitations. It was calibrated by the manufacturer against unconfined compression tests made on "silty clays and clayey soils." Correlation of penetrometer values against unconfined tests of Missouri soils show marked disagreement, with penetrometer values almost always exceeding unconfined values (this is believed, to a large extent, to be due to the effect of structure often found in Missouri soils). As the clay content increases, however, the correlation improves. For certain soil types and particularly in certain areas, more definite correlations are possible and may be of value. Obviously, penetrometer values in non-cohesive soils are meaningless and should not be recorded. 4. Pocket penetrations should be made on each cut surface throughout a sample and the range in readings indicated on the sampling log. Averages of several readings on a surface are preferable to just one. 5. Bear in mind that the pocket penetrometer is at best a crude instrument. Dirt about the plunger or the spring may influence readings. Springs get old. Checks indicate that various penetrometers deviate by a quarter ton or more in indicated values under the same load. 6. For Missouri soil the P c values are generally equal to the pocket penetrometer value in KSF + 1 KSF. Ex. (Pocket Penetrometer reading is 1 tsf, the P c = 1 tsf + 1 ksf = 3ksf). This can be a guide in setting up consolidation tests. If the calculated P 2 value at a certain depth under a proposed fill is, say 2.5 KSF, and the soil at that depth has a pocket penetrometer reading of 3.0 TSF, or 6.0 KSF, then that soil is obviously preconsolidated beyond the anticipated P 2 loading and a consolidation test would probably be a waste of money and time. Of course, if in doubt, make the test. C. Field Moistures 1. Field moisture samples should be taken immediately from undisturbed samples and sealed in tared moisture cans with tape. Excess moistures as is found about the wetted circumference of most samples should be trimmed away and the moisture sample should be taken from the interior of the sample. Moisture samples of saturated granular materials are of very little value as the moisture content will change with densification or loosening during sampling, extruding, and handling, as well as by draining freely in the case of sands. Moisture samples of a borderline material such as silt should be taken carefully to avoid disturbed zones.